Compared with inorganic lenses, plastic lenses have a low weight, are not easily cracked, and can be dyed, and thus, recently, have rapidly become widespread in optical elements such as eyeglass lenses and camera lenses.
For resins for plastic lenses, there has been a demand for additional improvement in performance, and there has been a demand for an increase in the refractive index, an increase in the Abbe number, a decrease in the specific weight, an improvement of the heat resistance, and the like. Thus far, a variety of resin materials for lenses have been developed and put into use.
Among them, optical materials comprised of sulfide-based resins have a high refractive index and a high Abbe number and are being studied as ultrahigh refractive index materials having a refractive index of higher than 1.6. Sulfide-based resins are obtained by polymerizing a polymerizable composition including an episulfide compound (Patent Documents 1 to 4). In recent years, a variety of studies also have been carried out in order to improve the quality of episulfide compounds and resins for optical materials obtained from the episulfide compounds (Patent Documents 5 and 6).
Regarding epichlorohydrin as well which is a raw material of episulfide compounds, a producing route in which epichlorohydrin is synthesized by means of chlorination and epoxidation of glycerin originating from natural products has been developed instead of a producing route in which epichlorohydrin is synthesized from a fossil raw material (propylene, allyl alcohol, or the like) of the related art and the application of the producing route to epoxy resins and the like is being studied (Patent Document 7). However, no studies are being carried out regarding optical material use.
As plastic lens materials obtained using plant-derived materials, an eyeglass lens which includes a polycarbonate resin having a constituent unit derived from isosorbide as a main component and is obtained by means of injection molding is proposed (Patent Document 8). This enables the preparation of optical lenses having high heat resistance, high strength, and low distortion which are produced from plant-derived materials, but there is room for improvement in optical properties such as the refractive index.
Furthermore, in Patent Document 9, a resin comprised of plant-derived materials is proposed, but this resin is not for use as an ultrahigh refractive index material having a refractive index of higher than 1.6, and any optical properties and the like of the obtained resin are not exhibited.